为什么我失去了数据，我已经存储当我改变类在java

Question

我编写了一个简单的邮件系统代码。该系统由四个类组成:

列表项
用户
• 用户(主类)
• 邮件组

我的问题是关于高年级的。在我的代码中，将从Users类开始，并弹出一个菜单，您可以在其中添加，删除系统作为LinkedList。此外，在菜单中有一个使用选项，它将从系统中选择一个现有用户，并弹出位于user类中的另一个菜单。在这个类中，有一个特定用户拥有的电子邮件的另一个LinkedList。在新的菜单中，还有列表电子邮件、阅读电子邮件和发送电子邮件等选项。我的问题从这里开始。我可以发送消息，但不能列出消息。如果我在User类中调用look()方法，它将显示0条消息，但如果在主类中调用它，它将显示消息。请给我一些建议。谢谢你。

我的代码:用户类

public class Users 
{
public static void main(String[] args)
{
    new Users();
}
private LinkedList<User> users = new LinkedList<User>();
private User user;
private Email email;
public Users()
{   menu();}
private void menu()
{   char c = readChoice();
    while (!isEnd(c))
    {   execute(c);
        c = readChoice();}}
private char readChoice()
{   System.out.print("Choice (a/d/g/u/x): ");
    return In.nextChar();}  
private void execute(char c)
{   switch(c)
    {   case 'a': add(); break;
        case 'd': delete(); break;
        case 'g': break;
        case 'u': use(); break;
        default : System.out.println("    Invalid choice");}}
private void use()
{   User user = new User(this);
    if (exists(user.getName()))
        user.use();
    else
        System.out.println("    No such user"); }
public void send()
{   User user = user(readRecipient());
    String header = readHeader();
    String message = readMessage();
    if (user != null)
    {    user.add(new Email(user, header, message));}
        //user.look();this method is just for tes if it is included
                    // in the method above it lists the messages.
    else
        System.out.println("No such adress");}
}

My User class

public class User 
{
private String name;
private Users users;
private LinkedList<Email> emails = new LinkedList<Email>();
public User(Users users)
{   this.users = users;
    this.name = readName();}
public void use()
{   char c = readChoice();
    while (!isEnd(c))
    {   execute(c);
        c = readChoice();}}
private char readChoice()
{   System.out.print("  Choice (l/r/s/d/x): ");
    return In.nextChar();}
private void execute(char c)
{   switch(c)
    {   case 'l': look(); break;
        case 'r': read(); break;
        case 's': send(); break;
        default : System.out.println("    Invalid choice");}}
public void look()
{   String s = "    ";
    s += name + " has " + emailSize() + " messages";
    System.out.println(s);}
public void add(Email email)
{   emails.add(email);}
private void send()
{   users.send();}
}

最后一堂课Email:

package assignment;
public class Email {
private String header;
private String message;
private User user;
public Email(User user, String header, String message)
{   this.user = user;
    this.header = header;
    this.message = message;}

}

Answer 1

您的send方法将电子邮件属性为收件人并相应地执行:

public void send()
{   User user = user(readRecipient());
    String header = readHeader();
    String message = readMessage();
    if (user != null)
    {    user.add(new Email(user, header, message));
        user.look();}
    else
        System.out.println("No such adress");}
}

呼叫user.look()，用户是User user = user(readRecipient());

所以如果你想比较"苹果和苹果"，你需要选择收件人当你使用"l"选项。